Bioabsorbable Stent Having a Radiopaque Marker

ABSTRACT

A bioabsorbable stent includes one or more radiopaque markers. The stent body may include a generally cylindrical body portion and a marker support for receiving the one or more marker(s). The marker support may be connected to an end of the body portion, or may be an integral portion of the body portion. By selectively controlling dissolution of the biodegradable material of the marker support, the marker support will remain intact for a sufficient time to allow for the marker to endothelialize and therefore prevent the marker from dislodging and embolizing. The controlled dissolution may be accomplished via one or more of the following mechanisms, including increasing the cross-sectional thickness of the marker support, passivating or oxidizing the marker support, utilizing a different, slower absorbing material for the marker support, utilizing a bioabsorbable polymeric coating on the marker support, or protecting the marker support with a sacrificial anode.

FIELD OF THE INVENTION

The invention relates generally to temporary endoluminal prostheses forplacement in a body lumen, and more particularly to stents that arebioabsorbable.

BACKGROUND OF THE INVENTION

A wide range of medical treatments exist that utilize “endoluminalprostheses.” As used herein, endoluminal prostheses is intended to covermedical devices that are adapted for temporary or permanent implantationwithin a body lumen, including both naturally occurring and artificiallymade lumens, such as without limitation: arteries, whether locatedwithin the coronary, mesentery, peripheral, or cerebral vasculature;veins; gastrointestinal tract; biliary tract; urethra; trachea; hepaticshunts; and fallopian tubes.

Accordingly, a wide assortment of endoluminal prostheses have beendeveloped, each providing a uniquely beneficial structure to modify themechanics of the targeted lumen wall. For example, stent prostheses areknown for implantation within body lumens to provide artificial radialsupport to the wall tissue, which forms the various lumens within thebody, and often more specifically, for implantation within the bloodvessels of the body.

Essentially, stents that are presently utilized are made to bepermanently or temporarily implanted. A permanent stent is designed tobe maintained in a body lumen for an indeterminate amount of time and istypically designed to provide long term support for damaged ortraumatized wall tissues of the lumen. There are numerous conventionalapplications for permanent stents including cardiovascular, urological,gastrointestinal, and gynecological applications. A temporary stent isdesigned to be maintained in a body lumen for a limited period of timein order to maintain the patency of the body lumen, for example, aftertrauma to a lumen caused by a surgical procedure or an injury.

Permanent stents, over time, may become encapsulated and covered withendothelium tissues, for example, in cardiovascular applications,causing irritation to the surrounding tissue. Further, if an additionalinterventional procedure is ever warranted, a previously permanentlyimplanted stent may make it more difficult to perform the subsequentprocedure.

Temporary stents, on the other hand, preferably do not becomeincorporated into the walls of the lumen by tissue ingrowth orencapsulation. Temporary stents may advantageously be eliminated frombody lumens after an appropriate period of time, for example, after thetraumatized tissues of the lumen have healed and a stent is no longerneeded to maintain the patency of the lumen. As such, temporary stentsmay be removed surgically or be made bioabsorbable/biodegradable.

Temporary stents may be made from bioabsorbable and/or biodegradablematerials that are selected to absorb or degrade in vivo over time.However, there are disadvantages and limitations associated with the useof bioabsorbable or biodegradable stents. Limitations arise incontrolling the breakdown of the bioabsorbable materials from which suchstents are made, as in, preventing the material from breaking down tooquickly or too slowly. If the material is absorbed too quickly, thestent will not provide sufficient time for the vessel to heal, or ifabsorbed too slowly, the attendant disadvantages of permanentlyimplanted stents may arise.

There is a need for a temporary stent that provides sufficient supportin a body lumen for the duration of a therapeutically appropriate periodof time, which then degrades to be eliminated from the patient's bodywithout surgical intervention. Magnesium appears to be a suitablematerial for providing both strength and bioabsorbability to a stent. Amagnesium stent may handle like an ordinary metallic stent, because itplastically deforms and thus have limited recoil, but also may beengineered so as to be absorbable within the body. That is, such amagnesium stent has all the good handling characteristics of anon-biodegradable metal stent while still providing an absorbable stentplatform. Such magnesium stents, however, are not very radiopaquebecause magnesium does not show up well under fluoroscopy. Accordingly,it would be beneficial if such a magnesium bioabsorbable stent could bemade to be more radiopaque or visible under a fluoroscopic device.

It is known to utilize a radiopaque marker with an ordinary metallicstent to make the stent more visible under a fluoroscopic device.However, a problem that arises using a radiopaque marker with abiodegradable stent is a risk of embolism caused by the dislodgement ofthe marker that can then move downstream, which may occur when thebiodegradable stent is absorbed by the body, but the marker is not. Oncethe stent biodegrades, the marker may embolize and block the coronaryarteries, or migrate further downstream, causing additionalcomplications. Thus, it would be beneficial if such a bioabsorbablestent could be made to be more radiopaque without increasing the risk ofembolism caused by the dislodgement of the marker.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to an intraluminalstent device. In one embodiment of the invention, the stent has abiodegradable body portion having a proximal end, a distal end, and agenerally cylindrical hollow shape. The body portion has a firstthickness. The stent also includes at least one biodegradable markersupport having a second thickness and a radiopaque marker attached tothe marker support. The second thickness is greater than the firstthickness so that upon implantation of the stent within the vasculature,dissolution of the marker support is selectively controlled tobiodegrade slower than the remaining body portion of the stent in orderto allow the marker to endothelialize. The body portion and markersupport may be formed of magnesium or a magnesium alloy, and theradiopaque marker may be formed from tantalum.

In another embodiment of the invention, the stent has a biodegradablebody portion having a proximal end, a distal end, and a generallycylindrical hollow shape. The stent includes at least one biodegradablemarker support and a radiopaque marker attached to the marker support. Abioabsorbable coating is placed over at least a portion of the markersupport so that upon implantation of the stent within the vasculaturedissolution of the marker support is selectively controlled tobiodegrade slower than the remaining body portion of the stent in orderto allow the marker to endothelialize.

In another embodiment of the invention, the stent has a biodegradablebody portion having a proximal end, a distal end, and a generallycylindrical hollow shape. The stent includes at least one biodegradablemarker support and a radiopaque marker attached to the marker support. Acorrosion-resistant layer is formed by oxidizing or passivating at leasta portion of the marker support so that upon implantation of the stentwithin the vasculature dissolution of the marker support is selectivelycontrolled to biodegrade slower than the remaining body portion of thestent in order to allow the marker to endothelialize.

In another embodiment of the invention, the stent has a biodegradablebody portion having a proximal end, a distal end, and a generallycylindrical hollow shape. The stent also includes at least onebiodegradable marker support formed of a first biodegradable materialhaving a first corrosion potential and a radiopaque marker attached tothe marker support. A sacrificial anode is electrically connected to themarker support, wherein the sacrificial anode is formed of a secondbiodegradable material having a second corrosion potential that ishigher than the first corrosion potential of the marker support so thatupon implantation of the stent within the vasculature dissolution of themarker support is selectively controlled to biodegrade slower than thebody portion of the stent in order to allow the marker toendothelialize.

In another embodiment of the invention, the stent has a biodegradablebody portion having a proximal end, a distal end, and a generallycylindrical hollow shape. The body portion is formed of a firstbiodegradable material having a first dissolution rate. The stent alsoincludes at least one biodegradable marker support formed of a secondbiodegradable material having a second dissolution rate and a radiopaquemarker attached to the marker support. The second dissolution rate isslower than the first dissolution rate so that upon implantation of thestent within the vasculature dissolution of the marker support isselectively controlled to biodegrade slower than the remaining bodyportion of the stent in order to allow the marker to endothelialize.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following description of the invention as illustratedin the accompanying drawings. The accompanying drawings, which areincorporated herein and form a part of the specification, further serveto explain the principles of the invention and to enable a personskilled in the pertinent art to make and use the invention. The drawingsare not to scale.

FIG. 1 a perspective view of an exemplary stent in accordance with anembodiment of the present invention.

FIG. 2 is a plan view of a flattened stent strut in accordance with anembodiment of the present invention.

FIG. 3 is a plan view of a marker assembly in accordance with anembodiment of the present invention.

FIG. 4 is a cross-sectional view of the marker assembly taken along lineC-C of FIG. 3.

FIG. 5 is a cross-sectional view of the marker assembly taken along lineD-D of FIG. 3.

FIG. 6 is a cross-sectional view of a stent strut taken along line A-Aof FIG. 1.

FIG. 7 is a cross-sectional view of a marker support of the markerassembly taken along line B-B of FIG. 2.

FIG. 8 is a plan view of a flattened stent strut in accordance withanother embodiment of the present invention.

FIG. 9 is a cross-sectional view of a marker support of the markerassembly taken along line B-B of FIG. 2 in accordance with anotherembodiment of the present invention.

FIG. 10 is a cross-sectional view of a marker support of the markerassembly taken along line B-B of FIG. 2 in accordance with anotherembodiment of the present invention.

FIG. 11 is a cross-sectional view of the marker assembly taken alongline C-C of FIG. 3 in accordance with another embodiment of the presentinvention.

FIG. 12 is a cross-sectional view of a marker support of the markerassembly taken along line B-B of FIG. 2 in accordance with anotherembodiment of the present invention.

FIG. 13 is a plan view of a flattened stent strut in accordance withanother embodiment of the present invention.

FIG. 14 is a side elevational view of a stent delivery system inaccordance with an embodiment of the present invention.

FIG. 15 is a plan view of a flattened stent strut in accordance withanother embodiment of the present invention.

FIG. 16A is a cross-sectional view of the stent strut taken along lineA-A of FIG. 15 in accordance with an embodiment of the presentinvention.

FIG. 16B is a cross-sectional view of the stent strut taken along lineA-A of FIG. 15 in accordance with another embodiment of the presentinvention.

FIG. 17 is a plan view of a flattened stent strut having a markerassembly in accordance with another embodiment of the present invention.

FIG. 18A is a cross-sectional view of the marker assembly taken alongline A-A of FIG. 17 in accordance with an embodiment of the presentinvention.

FIG. 18B is a cross-sectional view of the marker assembly taken alongline A-A of FIG. 17 in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments of the present invention are now described withreference to the figures, wherein like reference numbers indicateidentical or functionally similar elements. The terms “distal” and“proximal” are used in the following description with respect to aposition or direction relative to the treating clinician. “Distal” or“distally” are a position distant from or in a direction away from theclinician. “Proximal” and “proximally” are a position near or in adirection toward the clinician.

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Although the description of the invention is in the contextof treatment of blood vessels such as the coronary, carotid and renalarteries, the invention may also be used in any other body passagewayswhere it is deemed useful. Furthermore, there is no intention to bebound by any expressed or implied theory presented in the precedingtechnical field, background, brief summary or the following detaileddescription.

Embodiments of the present invention relate to a bioabsorbable stenthaving one or more radiopaque markers that are visible to a physicianviewing, for example, an X-ray fluoroscopy device while deploying and/orpositioning the stent into the body vessel. Radiopaque markers aregenerally secured to the proximal and/or distal ends of the stentextending outwardly from one or more peaks or troughs of undulatingbands of the stent body. Embodiments of the present invention aredirected to underlying stent structures that allow the one or moremarkers to endothelialize. Because the stent bioresorbs or breaks downand the marker does not, it is important that the marker remains fixedand stable during bioresorption of the stent body. By controllingdissolution of an area of the stent near the marker, the marker mayendothelialize and is therefore prevented from dislodging andembolizing. Thus, the bioabsorbable stent may be made more radiopaquewithout increasing the risk of embolism caused by the dislodgement ofthe marker.

Dissolution of the biodegradable stent material or portion holding themarker in place (hereinafter referred to as marker support) iscontrolled or slowed so that it will remain intact for a sufficient timeto allow for marker endothelialization. The term “endothelialization” ismeant to describe the process in which a foreign object, such as themarker in embodiments of the present invention, becomes incorporatedinto the walls of the lumen by tissue ingrowth or encapsulation. Thus,in other words, dissolution of the marker support is controlled so thatthe marker is held against the vessel wall long enough toendothelialize. As part of the vessel wall, the marker is stable andwill not migrate downstream and thus avoids causing potentialcomplications. Dissolution of the marker support must be controlled orslowed for a sufficient time to allow for endothelialization to occur,approximately three to six weeks. The biodegradable body portion of thestent has a first dissolution rate and the marker support has a seconddissolution rate. The second dissolution rate is slower than the firstdissolution rate. In particular, the second dissolution rate isapproximately 30-100% slower than the first dissolution rate in order toallow the radiopaque marker to endothelialize. The controlleddissolution of the marker support may be accomplished via one or moremechanisms that include the following: increasing the cross-sectionalthickness of the marker support, passivating or oxidizing the markersupport, utilizing a different, slower absorbing material for markersupport, utilizing a bioabsorbable polymeric coating on the markersupport, anodically protecting the marker support with a sacrificialanode, and any other suitable means of slowing absorption or corrosionin the region that secures the marker.

In an embodiment of the present invention, rather than delay dissolutionof the entire stent in order to allow the radiopaque marker toendothelialize, it is desirable to selectively control or delaydissolution of only the stent material securing the marker. Selectivelycontrolling dissolution of only the marker support material allows theremainder of the stent body to be absorbed in a desired amount of timeand avoids the risk of the stent body becoming encapsulated and coveredwith endothelium tissues. In other words, if dissolution of the entirestent was controlled or delayed in order to allow the radiopaque markerto endothelialize, the stent body may also endothelialize and thus maynot break down as desired. The biodegradable stent body must be incontact with a body fluid such as blood in order for the stent tocorrode or be absorbed into the body as desired. Thus, selectivelycontrolling dissolution of only the marker support avoids theundesirable endothelialization of the stent body.

In one embodiment of the present invention, the biodegradable stent isformed of magnesium or a magnesium alloy and the marker is formed oftantalum. However, the marker may be formed of any other relativelyheavy metal which is generally visible by X-ray fluoroscopy such astantalum, titanium, platinum, gold, silver, palladium, iridium, and thelike. In addition, the stent may be formed of any suitable biodegradableor bioabsorbable material, including metals and polymers. Furtherdetails and description of the embodiments of the present invention areprovided below with reference to FIGS. 1-18B.

FIG. 1 illustrates an endoluminal prosthesis in accordance with anembodiment of the present invention. Stent 100 includes a generallycylindrical hollow body portion 106 extending between a proximal end 102and a distal end 104. Body portion 106 is configured to fit into a bodylumen such as a blood vessel. Stent 100 also includes at least onemarker assembly 120 which may be located at one or both ends of bodyportion 106. For example, in FIG. 1, marker assembly 120 is shown atproximal end 102 and at distal end 104. Marker assembly 120 includes amarker support 122 and a marker 130 that is formed of a radiopaquematerial which is visible to a physician viewing, for example, an X-rayfluoroscopy device while deploying and/or positioning stent 100 into thetarget body vessel, as described in detail below.

According to embodiments of the present invention, body portion 106 mayhave a generally tubular or cylindrical expandable structure and may becircularly symmetric with respect to a central longitudinal axis. Stent100 is a patterned tubular device that includes a plurality of radiallyexpandable cylindrical rings 108 aligned on a common longitudinal axisto form a generally cylindrical hollow body having a radial andlongitudinal axis. Cylindrical rings 108 may be formed from struts 110having a generally sinusoidal pattern including peaks 112, valleys 114,and generally straight segments 116 connecting peaks 112 and valleys114. Connecting links 118 connect adjacent cylindrical rings 108together. In FIG. 1, connecting links 118 are shown as generallystraight links connecting peak 112 of one ring 108 to valley 114 of anadjacent ring 108. However, connecting links 118 may connect a peak 112of one ring 108 to a peak 112 of an adjacent ring, or a valley 114 to avalley 114, or a straight segment 116 to a straight segment 116.Further, connecting links 118 may be curved. Connecting links 118 mayalso be excluded, with a peak 112 of one ring 108 being directlyattached to a valley 114 of an adjacent ring 108, such as by welding,soldering, or the manner in which stent 100 is formed, such as byetching the pattern from a flat sheet or a tube. An outer diameter ofbody portion 106 may be approximately equal to or slightly larger thanan inner diameter of a target body vessel and may be substantiallyconstant along the central longitudinal axis.

It will be appreciated by one of ordinary skill in the art that stent100 of FIG. 1 is merely an exemplary stent and that stents of variousforms and methods of fabrication can be used in accordance with variousembodiments of the present invention. For example, in a typical methodof making a stent, a thin-walled, small diameter metallic tube is cut toproduce the desired stent pattern, using methods such as laser cuttingor chemical etching. The cut stent may then be de-scaled, polished,cleaned and rinsed. Some examples of methods of forming stents andstructures for stents are shown in U.S. Pat. No. 4,733,665 to Palmaz,U.S. Pat. No. 4,800,882 to Gianturco, U.S. Pat. No. 4,886,062 to Wiktor,U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 5,292,331 to Boneau,U.S. Pat. No. 5,421,955 to Lau, U.S. Pat. No. 5,935,162 to Dang, U.S.Pat. No. 6,090,127 to Globerman, and U.S. Pat. No. 6,730,116 to Wolinskyet al., each of which is incorporated by reference herein in itsentirety. Further, balloon-expandable stents may also be utilized invarious embodiments of the present invention, such as those disclosed inU.S. Pat. No. 5,776,161 to Globerman, U.S. Pat. No. 6,113,627 to Jang,and U.S. Pat. No. 6,663,661 to Boneau, each of which is incorporated byreference herein in its entirety.

FIG. 2 shows a single stent strut 110 in accordance with an embodimentof the present invention. Stent strut 110 is shown as if the generallycylindrical ring 108 has been cut and the stent strut 110 has been laidout flat. Marker support 122 is shown attached to stent strut 110 viaconnection 228. In this embodiment, marker support 122 is an annular orring shape, having an inner or interior volume 224 and an outer orperipheral surface 226. Radiopaque marker 130 (not shown in FIG. 2) isreceived or located within inner volume 224 of the annular or ringshaped marker support 122. Marker support 122 may have any suitableshape, including circular or rectangular, as long as it is adapted toreceive radiopaque marker 130. Connection 228 may be formed by weldingstent strut 110 to marker support 122 such as by resistance welding,friction welding, laser welding or another form of welding such that noadditional materials are used to connect stent strut 110 and markersupport 122. Alternatively, stent strut 110 and marker support 122 canbe connected by soldering, by the addition of a connecting element therebetween, or by another mechanical method. Further, stent strut 110 andmarker support 122 may be formed pre-connected as a unitary structure,such as by laser cutting or etching the entire stent body from a hollowtube or sheet. Other connections or ways to connect stent strut 110 andmarker support 122 would be apparent to one skilled in the art and areincluded herein. To describe the particular structure of stent 100,stent strut 110 and marker support 122 may be described as beingconnected or coupled to each other. Thus, the terms “connect with,”“connected,” or “coupled” may mean either naturally continuing (orflowing together) or mechanically coupled together.

FIG. 3 is a plan view of marker assembly 120 including radiopaque marker130 received or located within inner volume 224 of the annular or ringshaped marker support 122. In order to ensure marker 130 is notdislodged from the stent body, marker 130 must remain securely fixed tomarker support 122 during delivery and deployment. Securement may beaccomplished via various mechanisms, including press fitting, diffusionbonding, crimping, and/or metallization coating.

Due to the respective materials of marker support 122 and marker 130,marker support 122 bioresorbs or dissociates in vivo and marker 130 doesnot. More particularly, body portion 106 of stent 100 (including stentstrut 110 and marker support 122) is constructed from a biodegradable orbioabsorbable material. In one embodiment, body portion 106 isconstructed out of magnesium or a magnesium alloy, includingformulations that have approximately 50-98% magnesium. A bioabsorbablemetal is preferred because of its greater structural strength.Alternatively, body portion 106 can be formed of a suitablebiodegradable or bioabsorbable polymer material, such as polyactic acid,polyglycolic acid, collagen, polycaprolactone, hylauric acid,co-polymers of these materials, as well as composites and combinationsthereof.

Marker 130 is formed of a radiopaque material that is visible to aphysician viewing, for example, an X-ray fluoroscopy device whiledeploying and/or positioning stent 100 into the target body vessel. Inone embodiment, marker 130 is formed of tantalum. However, marker 130may be formed from any suitable biocompatible material that enhances theradiopacity of stent 100, including tantalum, titanium, platinum, gold,silver, palladium, iridium, zirconium, barium, bismuth, and iodine.

In one embodiment of the present invention, as shown in FIGS. 3-5,marker 130 may include protrusions 332 on an outer surface 434 of marker130 in order to facilitate endothelialization of marker 130. FIG. 4 is across-sectional view of marker assembly 120 taken along line C-C of FIG.3, and FIG. 5 is a cross-sectional view of marker assembly 120 takenalong line D-D of FIG. 3. Protrusions 332 impart an irregular surface tothe marker 130, thereby enhancing friction between outer surface 434 ofmarker 130 and the vessel wall. The irregular surface provided byprotrusions 332 provides ingrowth sites for fibrotic tissue forretaining the marker 130 in place after implantation. Protrusions 332may have any suitable shape or configuration, for example, includinground, circular bumps as shown in FIGS. 3-5. Another configuration forprotrusions 332 may be rectangular ribs. Further, other configurationsmay be utilized for imparting an irregular surface onto marker 130 suchas indentations formed on outer surface 434 of marker 130. Each of thesestructures would provide sites for fibrotic tissue growth for markerretention. Outer surface 434 of marker 130 may be curved as shown inFIG. 4 in order to facilitate conformance to the vessel wall.

In another embodiment of the present invention, marker 130 may berelatively porous in order to facilitate endothelialization of marker130. For example, marker 130 may include a porous, tissue-engaging outersurface which promotes rapid tissue ingrowth and consequent markerstabilization. The porous surface may be formed by sintering orotherwise adhering small particles of metal or other granulated materialto the outer surface of marker 130. The sintered metallic material maybe the same material as that forming marker 130, or may be a differentmaterial. The porous surface may also be formed by dealloying and/orchemical etching processes known in the art. A relatively porous outersurface facilitates migration of cells (e.g. fibroblasts and endothelialcells) into and through marker 130 such that marker 130 may becomeincorporated into the walls of the lumen by tissue ingrowth.

As previously stated, due to the respective materials of body portion106 and marker 130, body portion 106 (including stent struts 110 andmarker support 122) bioresorbes or dissociates in vivo and marker 130does not. It is desirable to assure that marker 130 remains fixed andstable during bioresorption of body portion 106. Embodiments of thepresent invention are directed to selectively controlling dissolution ofmarker support 122 so that marker 130 may endothelialize and thereforebe prevented from dislodging and embolizing. Particularly dissolution ofthe biodegradable material of marker support 122 is controlled or slowedso that marker support 122 will remain intact a sufficient time to allowfor marker 130 to endothelialize, for example, three to six weeks. Thus,stent 100 may be made more radiopaque by the inclusion of marker 130without increasing the risk of embolism. The controlled dissolution maybe accomplished via one or more of the following mechanisms discussed inmore detail below, including increasing the cross-sectional thickness ofmarker support 122 relative to the cross-sectional thickness of stentstrut 110, utilizing a different, slower absorbing material for markersupport 122 relative to stent strut 110, passivating or oxidizing markersupport 122, utilizing a bioabsorbable polymeric coating on markersupport 122, anodically protecting marker support 122 with a sacrificialanode, or any other suitable means of slowing absorption or corrosion ofmarker support 122.

In one embodiment, the dissolution control mechanism is increasing thecross-sectional thickness of marker support 122 relative to thecross-sectional thickness of stent strut 110, as shown in FIGS. 6-7.FIG. 6 is a cross-sectional view of stent strut 110 taken along line A-Aof FIG. 1, while FIG. 7 is a cross-sectional view of marker support 122taken along line B-B of FIG. 2. As visible through a comparison of FIGS.6-7, stent strut 110 has a thickness T1 and marker support 122 has athickness T2, wherein T2 is greater than T1. Marker support 122 willthus bioresorb or break down in vivo slower than stent strut 110 due tothe increase in the amount of material at marker support 122.Accordingly, dissolution of the biodegradable material of marker support122 is controlled or slowed so that marker support 122 will remainintact for a sufficient time to allow for marker 130 to endothelialize.Thickness T2 may be selected such that the dissolution of marker support122 takes approximately three to six weeks and thus allows marker 130 toendothelialize.

In another embodiment of the present invention illustrated in FIG. 8,the dissolution control mechanism is forming marker support 822 andstent strut 810 from different biodegradable materials. Moreparticularly, stent strut 810 is formed from a first biodegradable orbioabsorbable material having a first dissolution rate. Marker support822 is formed from a second biodegradable or bioabsorbable materialhaving a second dissolution rate. The second dissolution rate is slowerthan the first dissolution rate so that marker support 822 may remainintact for a sufficient time for marker 830 to endothelialize. Each typeof bioabsorbable or biodegradable material has a characteristicdegradation rate in the body. Some materials are relativelyfast-bioabsorbing materials (weeks to months) while others arerelatively slow-bioabsorbing materials (months to years). By formingmarker support 822 of a different, slower absorbing material than stentstrut 810, the majority of the stent body will bioresorb or break downrelatively quickly while marker support 822 remains intact for asufficient time for marker 830 to endothelialize. For example, the stentstrut 810 may be constructed out of magnesium or a magnesium alloy,having a high percentage of magnesium. Marker support 822 may also beconstructed of a magnesium alloy. However, the alloy chemistry of markersupport 822 may be varied to produce a more noble alloy having a slowerdissolution rate, such as a combination of magnesium (Mg) alloyed withiron (Fe). Marker support 822 is shown attached to stent strut 810 viaconnection 828. For example, marker support 822 may be welded orotherwise mechanically attached to stent strut 810.

In another embodiment of the present invention, the dissolution controlmechanism is utilizing a bioabsorbable coating on marker support 122that delays dissolution of marker support 122. In one embodiment, thebioabsorbable coating may be formed from a polymeric material.Dissolution of the polymeric material may degrade over approximately twoto four weeks, at which point the biodegradable marker support 122 wouldbe exposed. The material of marker support 122 would then continue todegrade over the next two to four weeks, such that a total ofapproximately four to eight weeks passes before marker 130 ispotentially unsupported. As previously mentioned, approximately three tosix weeks is sufficient to allow for endothelialization to occur, andthus marker 130 will be part of the vessel wall once both the polymericcoating and the material of marker support 122 is absorbed by the body.The bioabsorbable polymeric material may include polymers or copolymerssuch as polylactide [poly-L-lactide (PLLA), poly-D-lactide (PDLA)],polyglycolide, polydioxanone, polycaprolactone, polygluconate,polylactic acid-polyethylene oxide copolymers, modified cellulose,collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester,poly(amino acids), poly(alpha-hydroxy acid) or related copolymersmaterials. The dissolution rate of the coating may be tailored bycontrolling the type of bioabsorbable polymer, the thickness and/ordensity of the bioabsorbable polymer, and/or the nature of thebioabsorbable polymer. For example, each type of bioabsorbable polymerhas a characteristic degradation rate in the body. Some materials arerelatively fast-bioabsorbing materials (weeks to months) while othersare relatively slow-bioabsorbing materials (months to years). Inaddition, increasing thickness and/or density of a polymeric materialwill generally slow the dissolution rate of the coating. Characteristicssuch as the chemical composition and molecular weight of thebioabsorbable polymer may also be selected in order to control thedissolution rate of the coating.

The coating may be applied to one or more surfaces of marker support 122in order to isolate one or more body fluid contacting surfaces of markersupport 122. For example, as shown in FIG. 9, a surface coating 940 isapplied to one surface of marker support 122. FIG. 9 is across-sectional view of marker support 122 taken along line B-B of FIG.2. When implanted into a target vessel, body fluid such as bloodcontacts stent 100 and acts as the corrosion agent. Preferably, surfacecoating 940 is applied to a select surface such that it prevents markersupport 122 from coming into contact with a body fluid and thereforedelays corrosion of marker support 122 until surface coating 940 iseroded. Surface coating 940 may additionally be applied to one or morebody fluid contacting surfaces of marker 130. Accordingly, dissolutionof the biodegradable material of marker support 122 is controlled orslowed so that marker support 122 will remain intact for a sufficienttime to allow for marker 130 to endothelialize.

In another embodiment of the present invention, an encapsulating coating1042 may also be utilized on marker support 122 as the dissolutioncontrol mechanism. For example, as shown in FIG. 10, encapsulatingcoating 1042 may be applied to all surfaces of marker support 122 inorder to isolate marker support 122. FIG. 10 is a cross-sectional viewof marker support 122 taken along line B-B of FIG. 2. Encapsulatingcoating 1042 prevents marker support 122 from coming into contact with abody fluid, and thus delays corrosion of marker support 122 untilencapsulating coating 1042 is eroded. Further as shown in FIG. 11, anencapsulating coating 1144 may be applied to marker assembly 120 suchthat the coating material encapsulates both marker support 122 andmarker 130. FIG. 11 is a cross-sectional view of marker assembly 120,including marker support 122 having marker 130 located therein, takenalong line C-C of FIG. 3. An encapsulating coating, such asencapsulating coating 1042 or encapsulating coating 1144, will controlor slow down dissolution of the biodegradable material of marker support122 so that marker support 122 will remain intact for a sufficient timeto allow for marker 130 to endothelialize.

In another embodiment of the present invention illustrated in FIG. 12,the dissolution control mechanism includes passivating or oxidizing oneor more body fluid contacting surfaces of marker support 122.Passivating or oxidizing marker support 122 forms a protectivecorrosion-inhibiting barrier or layer 1246 that prevents prematuredissolution of marker support 122. For example, as shown in FIG. 12,protective corrosion-inhibiting barrier or layer 1246 is formed on onesurface of marker support 122. FIG. 12 is a cross-sectional view ofmarker support 122 taken along line B-B of FIG. 2. When implanted into atarget vessel, body fluid such as blood contacts stent 100 and acts asthe corrosion agent. Preferably, protective corrosion-inhibiting barrieror layer 1246 is formed to a select surface such that it delayscorrosion of marker support 122 until protective corrosion-inhibitingbarrier or layer 1246 is eroded. Accordingly, dissolution of thebiodegradable material of marker support 122 is controlled or slowed sothat marker support 122 will remain intact for a sufficient time toallow for marker 130 to endothelialize. For example, when marker support122 is formed from magnesium, a solution of nitric oxide, chromic acid,or hydrofluoric (HF) acid may be utilized to oxidize material of markersupport 122. In addition, electropolishing techniques may also beutilized to passivate or oxidize marker support 122.

In another embodiment of the present invention illustrated in FIG. 13,the dissolution control mechanism is anodically protecting markersupport 122 with a sacrificial anode 1350 having a higher corrosionpotential than marker support 122. Sacrificial anode 1350 iselectrically connected to marker support 122 so that an electricalpathway occurs between sacrificial anode 1350 and marker support 122.Due to the higher corrosion potential of sacrificial anode 1350,electrolytic galvanic corrosion of marker support 122 is redirected tosacrificial anode 1350, away from marker support 122, such thatdissolution of the material of the marker support is delayed for asufficient time for marker 130 to endothelialize. Therefore, the use ofdesignated sacrificial anode 1350 will control or slow down dissolutionof the biodegradable material of marker support 122 so that markersupport 122 will remain intact for a sufficient time to allow for marker130 to endothelialize. Thus, the amount of sacrificial anode 1350utilized should preferably be sufficient to remain intact for a desiredduration of time to permit complete endothelialization of marker 130.

As shown in the embodiment of FIG. 13, the sacrificial anode 1350 may bein the form of a tab adjacent marker support 122 which is electricallyconnected to marker support 122 by a tether or connector 1352. One ormore sacrificial anode 1350 may be provided. More generally, one or moresacrificial anode portions may be provided at one or both ends of thestent or at any other suitable location in the stent as long as thesacrificial anode portions are electrically connected to marker support122. In another embodiment, the sacrificial anode 1350 may be in theform of metal plating or a coating on a portion of marker support 122 oraffixed, attached, or otherwise electrically connected to marker support122. As apparent to one of ordinary skill in the art, in order forsacrificial anode 1350 to be electrically connected to marker support122, it is not required that sacrificial anode 1350 be mechanicallyconnected to marker support 122. For example, a body fluid such as bloodmay act to electrically connect sacrificial anode 1350 to marker support122 without a mechanical connection between the two structures.

Any suitable material may be selected for sacrificial anode 1350 so longas the material has a higher corrosion potential than marker support122. Materials utilized for the sacrificial anode 1350 may include butare not limited to magnesium or a magnesium alloy, zinc or a zinc alloy,a beryllium alloy, a lithium alloy, or an alloy containing two or moreor the previously mentioned elements. The material selected for thesacrificial anode 1350 functions as an anode with respect to markersupport 122 while the material for marker support 122 is, in turn, acathode with respect to the sacrificial anode 1350. For example,sacrificial anode 1350 may be formed from 100% magnesium while markersupport 122 is formed from a magnesium alloy.

Body portion 106 of stent 100 may be formed using any of a number ofdifferent methods. For example, body portion 106 may be formed bywinding a wire or ribbon around a mandrel to form a strut pattern likethose described above and then welding or otherwise mechanicallyconnecting two ends thereof to form a cylindrical ring 108. A pluralityof cylindrical rings 108 are subsequently connected together to formbody portion 106. Alternatively, body portion 106 may be manufactured bymachining tubing or solid stock material into toroid bands, and thenbending the bands on a mandrel to form the pattern described above. Aplurality of cylindrical rings formed in this manner are subsequentlyconnected together to form the longitudinal stent body. Laser orchemical etching or another method of cutting a desired shape out of asolid stock material or tubing may also be used to form body portion 106of the present invention. In this manner, a plurality of cylindricalrings may be formed connected together such that the stent body is aunitary structure. Further, body portion 106 of the present inventionmay be manufactured in any other method that would be apparent to oneskilled in the art. The cross-sectional shape of stent 100 may becircular, ellipsoidal, rectangular, hexagonal rectangular, square, orother polygon, although at present it is believed that circular orellipsoidal may be preferable.

Preferably, stent 100 is formed in an expanded state, crimped onto aconventional balloon dilation catheter for delivery to a treatment siteand expanded by the radial force of the balloon. Conventional ballooncatheters that may be used in the present invention includes any type ofcatheter known in the art, including over-the-wire catheters,rapid-exchange catheters, core wire catheters, and any other appropriateballoon catheters. For example, conventional balloon catheters such asthose shown or described in U.S. Pat. Nos. 6,736,827; 6,554,795;6,500,147; and 5,458,639, which are incorporated by reference herein intheir entirety, may be used within the stent delivery catheter of thepresent invention.

For example, FIG. 14 is an illustration of a stent delivery system 1401for tracking stent 100 to the target site in accordance with anembodiment of the present invention. Stent delivery system 1401 includesa catheter 1403 having a proximal shaft 1405, a guidewire shaft 1415,and a balloon 1407. Proximal shaft 1405 has a proximal end attached to ahub 1409 and a distal end attached to a proximal end of balloon 1407.Guidewire shaft 1415 extends between hub 1409 and a distal tip ofcatheter 1403 through proximal shaft 1405 and balloon 1407. Hub 1409includes an inflation port 1411 for coupling to a source of inflationfluid. Inflation port 1411 fluidly communicates with balloon 1407 via aninflation lumen (not shown) that extends through proximal shaft 1405. Inaddition, hub 1409 includes a guidewire port 1413 that communicates witha guidewire lumen (not shown) of guidewire shaft 1415 for receiving aguidewire 1417 there through. As described herein, guidewire shaft 1415extends the entire length of catheter 1403 in an over-the-wireconfiguration. However, as would be understood by one of ordinary skillin the art, guidewire shaft 1415 may alternately extend only within thedistal portion of catheter 1403 in a rapid-exchange configuration. Astent 100 having at least one marker assembly 120 attached theretoformed in accordance with an embodiment of the present invention ispositioned over balloon 1407. If desired, a sheath (not shown) may beprovided to surround stent 100 to facilitate tracking of the stentdelivery system 1401 over guidewire 1417 through the vasculature to asite of a stenotic lesion.

Deployment of balloon expandable stent 100 is accomplished by trackingcatheter 1403 through the vascular system of the patient until stent 100is located within a target vessel. The treatment site may include targettissue, for example, a lesion which may include plaque obstructing theflow of blood through the target vessel. Once positioned, a source ofinflation fluid is connected to inflation port 1411 of hub 1409 so thatballoon 1407 may be inflated to expand stent 100 as is known to one ofordinary skill in the art. Balloon 1407 of catheter 1403 is inflated toan extent such that stent 100 is expanded or deployed against thevascular wall of the target vessel to maintain the opening. Stentdeployment can be performed following treatments such as angioplasty, orduring initial balloon dilation of the treatment site, which is referredto as primary stenting.

As will be apparent to those of ordinary skill in the art, rather thanbeing disposed within an inner volume of an annular or ring shapedmarker support, the marker may be disposed on a flat, tab-like markersupport. As illustrated in FIG. 17, 18A, and 18B, marker 1730 may be inthe form of a metal plate or band on a portion of a marker support 1722or affixed, attached, or otherwise engaged to marker support 1722.Marker support 1722 has a flat, tab-like structure and may have anysuitable shape including circular or rectangular. Marker 1730 may beaffixed to marker support 1722 via the use of adhesives, laser weldingtechniques or other welding techniques or swaged onto marker support1722. Marker 1730 may be disposed on an outer surface 1870 of markersupport 1722, as shown in FIG. 18A. In another embodiment, marker 1730may be disposed within a recess 1872 of marker support 1722 as shown inFIG. 18B. Endothelialization of marker 1730 disposed in recess 1872would occur due to tissue ingrowth into and through marker 1730 suchthat marker 1730 may become incorporated into the walls of the lumen,including, for example, when marker 1730 has a relatively porous outersurface or contains protrusions or indentations on the outer surface inorder to facilitate tissue ingrowth. The controlled dissolution ofmarker support 1722 may be accomplished via various mechanisms discussedin more detail above, including increasing the cross-sectional thicknessof marker support 1722 relative to the cross-sectional thickness ofstent strut 1710, utilizing a different, slower absorbing material formarker support 1722 relative to stent strut 1710, passivating oroxidizing marker support 1722, utilizing a bioabsorbable polymericcoating on marker support 1722, anodically protecting marker support1722 with a sacrificial anode, or any other suitable means of slowingabsorption or corrosion of marker support 1722.

In addition, as will be apparent to those of ordinary skill in the art,rather than being adjacent to a body portion of the stent, the markersupport may be formed integrally with the body portion. For example, theradiopaque marker may be disposed on or within a stent strut of the bodyportion. In other words, as illustrated in FIG. 15, 16A, and 16B, stentstrut 1510 includes a first or marker support portion 1556 and a secondor remaining portion 1558. The marker support is formed integrally withthe first portion 1556 of stent strut 1510 and dissolution of theintegral marker support/first portion 1556 is selectively controlled tobiodegrade slower than the second portion 1558 of stent strut 1510 inorder to allow time for marker 1530 to endothelialize. Marker 1530 maybe in the form of a metal plate or band that is affixed, attached, orotherwise engaged to stent strut 1510. In FIG. 15, marker 1530 isaffixed to a straight portion 1516 but may alternatively or additionallybe affixed to peaks 1512 and/or valleys 1514. Further, marker 1530 isshown as a straight metal plate or band attached to stent strut 1510.However, marker 1530 may be any shape, such as circular, rectangular,oval, or a curvy strip. In addition, marker 1530 may be a metal plate orband wound or wrapped around the outer surface of stent strut 1510 in ahelical fashion. Marker 1530 may be affixed to stent strut 1510 via theuse of adhesives, laser welding techniques or other welding techniquesor swaged onto stent strut 1510. Marker 1530 may be disposed on an outersurface 1660 of stent strut 1510, as shown in FIG. 16A. In anotherembodiment, marker 1530 may be fully or partially disposed within arecess 1662 of stent strut 1510 as shown in FIG. 16B. Endothelializationof marker 1530 disposed in recess 1662 would occur due to tissueingrowth into and through marker 1530 such that marker 1530 may becomeincorporated into the walls of the lumen, including, for example, whenmarker 1530 has a relatively porous outer surface or containsprotrusions or indentations on the outer surface in order to facilitatetissue ingrowth. When the marker support is formed integrally with firstportion 1556 of stent strut 1510, controlled dissolution of the integralmarker support/first portion 1556 may be accomplished via variousmechanisms, including increasing the cross-sectional thickness of theintegral marker support/first portion 1556 of the stent strut securingthe marker versus the thickness of the second portion 1558 of the stentstrut, utilizing a different, slower absorbing material for the integralmarker support/first portion 1556 of the stent strut securing themarker, passivating or oxidation the integral marker support/firstportion 1556 of the stent strut securing the marker, utilizing abioabsorbable polymeric coating on the integral marker support/firstportion 1556 of the stent strut securing the marker, and/or anodicallyprotecting the integral marker support/first portion 1556 of the stentstrut securing the marker with a sacrificial anode, as described in moredetail above.

While various embodiments according to the present invention have beendescribed above, it should be understood that they have been presentedby way of illustration and example only, and not limitation. It will beapparent to persons skilled in the relevant art that various changes inform and detail can be made therein without departing from the spiritand scope of the invention. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the appendedclaims and their equivalents. It will also be understood that eachfeature of each embodiment discussed herein, and of each reference citedherein, can be used in combination with the features of any otherembodiment. All patents and publications discussed herein areincorporated by reference herein in their entirety.

1. An intraluminal stent device, comprising: a biodegradable bodyportion having a proximal end, a distal end, and a generally cylindricalhollow shape, wherein the body portion has a first thickness; at leastone biodegradable marker support having a second thickness; and aradiopaque marker attached to the marker support, wherein the secondthickness is greater than the first thickness so that upon implantationof the stent within the vasculature dissolution of the marker support isselectively controlled to biodegrade slower than the body portion of thestent in order to allow the marker to endothelialize.
 2. Theintraluminal stent device of claim 1, wherein the marker supportbiodegrades between 30-100% slower than the body portion of the stent.3. The intraluminal stent device of claim 1, wherein the body portionand marker support are of a biodegradable material selected from a groupconsisting of magnesium and a magnesium alloy and the radiopaque markeris formed from tantalum.
 4. The intraluminal stent device of claim 1,wherein an outer surface of the radiopaque marker includes an irregularsurface in order to facilitate endothelialization of the radiopaquemarker, the irregular surface being selected from a group consisting ofa surface including protrusions thereon, a surface includingindentations thereon, and a relatively porous surface.
 5. Theintraluminal stent device of claim 1, wherein the at least one markersupport has a configuration selected from the group consisting of anannular shape or a flat tab and is connected to one of the proximal endand the distal end of the body portion.
 6. The intraluminal stent deviceof claim 1, wherein the marker support is an integral portion of thebody portion of the stent.
 7. An intraluminal stent device, comprising:a biodegradable body portion having a proximal end, a distal end, and agenerally cylindrical hollow shape; at least one biodegradable markersupport; a radiopaque marker attached to the marker support; and abioabsorbable coating placed over at least a portion of the markersupport so that upon implantation of the stent within the vasculaturedissolution of the marker support is selectively controlled tobiodegrade slower than the body portion of the stent in order to allowthe marker to endothelialize.
 8. The intraluminal stent device of claim7, wherein the coating is a polymeric coating.
 9. The intraluminal stentdevice of claim 9, wherein the coating is encapsulates the markersupport.
 10. The intraluminal stent device of claim 9, wherein thecoating is placed over a surface of the marker support to isolate themarker support from contacting a body fluid.
 11. The intraluminal stentdevice of claim 7, wherein the body portion and marker support are of abiodegradable material selected from a group consisting of magnesium anda magnesium alloy and the radiopaque marker is formed from tantalum. 12.The intraluminal stent device of claim 7, wherein an outer surface ofthe radiopaque marker includes an irregular surface in order tofacilitate endothelialization of the radiopaque marker, the irregularsurface being selected from a group consisting of a surface includingprotrusions thereon, a surface including indentations thereon, and arelatively porous surface.
 13. The intraluminal stent device of claim 7,wherein the at least one marker support has a configuration selectedfrom the group consisting of an annular shape or a flat tab and isconnected to one of the proximal end and the distal end of the bodyportion.
 14. The intraluminal stent device of claim 7, wherein themarker support is an integral body of the body portion of the stent. 15.An intraluminal stent device, comprising: a biodegradable body portionhaving a proximal end, a distal end, and a generally cylindrical hollowshape; at least one biodegradable marker support; a radiopaque markerattached to the marker support; and a corrosion-resistant layer formedby oxidizing or passivating at least a portion of the marker support sothat upon implantation of the stent within the vasculature dissolutionof the marker support is selectively controlled to biodegrade slowerthan the body portion of the stent in order to allow the marker toendothelialize.
 16. The intraluminal stent device of claim 15, whereinthe body portion and marker support are of a biodegradable materialselected from a group consisting of magnesium and a magnesium alloy andthe radiopaque marker is formed from tantalum.
 17. The intraluminalstent device of claim 15, wherein an outer surface of the radiopaquemarker includes an irregular surface in order to facilitateendothelialization of the radiopaque marker, the irregular surface beingselected from a group consisting of a surface including protrusionsthereon, a surface including indentations thereon, and a relativelyporous surface.
 18. The intraluminal stent device of claim 15, whereinthe at least one marker support has a configuration selected from thegroup consisting of an annular shape or a flat tab and is connected toone of the proximal end and the distal end of the body portion.
 19. Theintraluminal stent device of claim 15, wherein the marker support is anintegral portion of the body portion of the stent.
 20. An intraluminalstent device, comprising: a biodegradable body portion having a proximalend, a distal end, and a generally cylindrical hollow shape; at leastone biodegradable marker support formed of a first biodegradablematerial having a first corrosion potential; a radiopaque markerattached to the marker support; and a sacrificial anode electricallyconnected to the marker support, wherein the sacrificial anode is formedof a second biodegradable material having a second corrosion potentialthat is higher than the first corrosion potential of the marker supportso that upon implantation of the stent within the vasculaturedissolution of the marker support is selectively controlled tobiodegrade slower than the body portion of the stent in order to allowthe marker to endothelialize.
 21. The intraluminal stent device of claim20, wherein the body portion and marker support are of a biodegradablematerial selected from a group consisting of magnesium and a magnesiumalloy and the radiopaque marker is formed from tantalum.
 22. Theintraluminal stent device of claim 20, wherein an outer surface of theradiopaque marker includes an irregular surface in order to facilitateendothelialization of the radiopaque marker, the irregular surface beingselected from a group consisting of a surface including protrusionsthereon, a surface including indentations thereon, and a relativelyporous surface.
 23. The intraluminal stent device of claim 20, whereinthe at least one marker support has a configuration selected from thegroup consisting of an annular shape or a flat tab and is connected toone of the proximal end and the distal end of the body portion.
 24. Theintraluminal stent device of claim 20, wherein the marker support is anintegral portion of the body portion of the stent.
 25. An intraluminalstent device, comprising: a biodegradable body portion having a proximalend, a distal end, and a generally cylindrical hollow shape, wherein thebody portion is formed of a first biodegradable material having a firstdissolution rate; at least one biodegradable marker support formed of asecond biodegradable material having a second dissolution rate; and aradiopaque marker attached to the marker support, wherein the seconddissolution rate is slower than the first dissolution rate so that uponimplantation of the stent within the vasculature dissolution of themarker support is selectively controlled to biodegrade slower than thebody portion of the stent in order to allow the marker toendothelialize.